diff --git a/python/packages/core/agent_framework/openai/_responses_client.py b/python/packages/core/agent_framework/openai/_responses_client.py
index 5aa9cc1a15..3cc69d2aaf 100644
--- a/python/packages/core/agent_framework/openai/_responses_client.py
+++ b/python/packages/core/agent_framework/openai/_responses_client.py
@@ -673,10 +673,18 @@ class RawOpenAIResponsesClient(  # type: ignore[misc]
                 if message.role == "assistant":
                     last_assistant_idx = idx
 
-            # Only include messages after the last assistant message
-            # This ensures we only send NEW user messages, not the full history
+            # When using previous_response_id, filter out assistant and function result messages
+            # but keep system/developer/user messages (the API accepts these roles)
             if last_assistant_idx >= 0:
-                chat_messages = chat_messages[last_assistant_idx + 1 :]
+                # Collect system/developer messages from before the last assistant
+                system_messages = [
+                    msg for msg in chat_messages[:last_assistant_idx] 
+                    if msg.role in ("system", "developer")
+                ]
+                # Get all messages after the last assistant (new user messages)
+                new_messages = chat_messages[last_assistant_idx + 1 :]
+                # Combine: system messages + new messages
+                chat_messages = system_messages + list(new_messages)
 
         list_of_list = [self._prepare_message_for_openai(message, call_id_to_id) for message in chat_messages]
         # Flatten the list of lists into a single list
diff --git a/python/packages/core/tests/openai/test_openai_responses_client.py b/python/packages/core/tests/openai/test_openai_responses_client.py
index f9bf1c3dfb..066882d91e 100644
--- a/python/packages/core/tests/openai/test_openai_responses_client.py
+++ b/python/packages/core/tests/openai/test_openai_responses_client.py
@@ -2117,18 +2117,19 @@ async def test_message_filtering_with_previous_response_id() -> None:
         ChatMessage(role="user", text="What's my name?"),
     ]
     
-    # When using previous_response_id, only new messages after last assistant should be included
+    # When using previous_response_id, assistant messages should be filtered but system messages preserved
     options = await client._prepare_options(
         messages, 
         {"conversation_id": "resp_12345"},  # Using resp_ prefix
     )  # type: ignore
     
-    # Should only include the last user message
+    # Should include: system message + last user message
     assert "input" in options
     input_messages = options["input"]
-    assert len(input_messages) == 1
-    assert input_messages[0]["role"] == "user"
-    assert "What's my name?" in str(input_messages[0])
+    assert len(input_messages) == 2, f"Expected 2 messages (system + user), got {len(input_messages)}"
+    assert input_messages[0]["role"] == "system"
+    assert input_messages[1]["role"] == "user"
+    assert "What's my name?" in str(input_messages[1])
     
     # Verify previous_response_id is set
     assert options["previous_response_id"] == "resp_12345"